1. Field of the Invention
The present invention relates to a radiation image acquisition method and apparatus, and more particularly to a radiation image acquisition method and apparatus wherein a radiation image recorded on a radiation image conversion panel is obtained as a digital image signal, further comprising a cell interval detection method and apparatus therefor.
2. Description of the Related Art
The use of a stimulable phosphor in recording radiation images as an alternative to the method of recording radiation images employing conventional photographic film and a sensitized screen is well known. In this method, an radiation image conversion panel (also called a stimulable phosphor sheet) having on the surface thereof a stimulable phosphor layer (herein after referred to as a phosphor layer) containing stimulable phosphor, absorbs energy from radiation passing through the body of a subject or emitted by a subject to record a latent image representing a radiation image. Afterwards, the stimulable phosphor is exposed to stimulating electromagnetic energy such as visible or infrared light, causing the energy from the radiation accumulated thereon to be emitted as light. In this specification, the light emitted from the stimulable phosphor upon stimulation thereof will be referred to as xe2x80x9cstimulated emissionxe2x80x9d. This stimulated emission is then read out as photoelectrical signals and reproduced as a visible image. After the radiation image has been read out from the phosphor layer, the energy stored thereon is erased and the radiation image conversion panel is reused for recording and reproducing radiation images in the same way.
It is preferable that the radiation image conversion panel described above be highly sensitive and capable of reproducing high-image quality radiation images. In particular, the ability to reproduce high-resolution X-ray images, which are the representative diagnostic-use radiation image, is desirable.
However, the stimulating light employed for reading out the radiation image stored in the phosphor layer of the radiation image conversion panel is dispersed within the phosphor layer, causing a degradation in image resolution. That is to say, the beam of stimulating light focused on the inner surface of the phosphor layer is scanned in the main and a sub-scanning directions, and the stimulated emission caused thereby to be emitted from the phosphor sheet is sequentially focused and read out; however, if the stimulating light irradiating the phosphor layer is dispersed horizontally therein, the stimulable phosphor on the periphery of the irradiation range (the scan spot) of the stimulating light are also stimulated as a result, causing the stimulable phosphor outside of the irradiation range of the stimulating light to emit stimulated emission, which is then detected as stimulated emission from within the irradiation range of the stimulating light, and the resolution of the image data of the latent image stored in the phosphor layer is deteriorated.
In order to avoid this phenomenon, a method is known wherein partition walls composed of a material impermeable to the stimulating light are disposed so as to partition the phosphor layer into a one- or two-dimensional fine grid along the plane of the panel, and the plurality of small compartments (hereinafter referred to as cells) formed by these partition walls are filled in with stimulable phosphor, forming columns or belts (as in for example, Japanese Unexamined Patent Publication No. 62(1986)-36600). In a phosphor layer having these cells arranged in the horizontal orientation thereof//spread across the plane thereof, the stimulating light is limited by the impermeable material of which the cell partition walls are formed and is not dispersed outside of a cell it enters, and the emission of stimulated emission outside of the irradiation range of the stimulating light can thereby be prevented. Therefore, the quantity of stimulated emission emitted from each cell corresponds to a value of one pixel of when the radiation image described above is to be reproduced, and when the image is read out from the phosphor layer, the radiation image reproduced has a high resolution, which is beneficial.
Note that aforementioned xe2x80x9cmaterial impermeable to stimulating lightxe2x80x9d is not limited to a material which cuts off the stimulating light completely, but refers to a material for which it is relatively difficult, compared to the stimulable phosphor packed within the cells, for the stimulating light to penetrate (preferably, substantially difficult for the stimulating light to penetrate).
However, although the cells forming the phosphor layer have a cyclical structure, the pitch of each cell is uneven. When stimulating light is irradiated onto the phosphor sheet having cells with an uneven construction, the quantity of stimulated emission from each cell corresponds to a value of one pixel when the radiation image described above is to be reproduced, and when the image is read out from the phosphor layer, aside from the change in the quantity of stimulated emission emitted in proportion to the quantity of radiation energy accumulated on the phosphor sheet, the quantity of stimulated emission changes depending on the unevenness of the pitch of the cells, and this causes a degradation in the image quality of the reproduced radiation image. For example, even if every region of the phosphor sheet is exposed to a strong beam of stimulating light of a uniform intensity, a fixed quantity of stimulated emission will not be emitted from each cell, and if a value of one pixel is assigned corresponding to the light emitted from each cell, a blurred image will be reproduced.
In view of the foregoing observations and description, the primary objective of the present invention is to provide a radiation image acquisition method and apparatus in which even if the pitch of the cells of the phosphor layer are uneven, the quantity of stimulated emission emitted from each cell can be acquired precisely as a digital image signal. The second objective of the present invention is to provide a cell interval detection method for aforementioned radiation image acquisition method and apparatus capable of precise detection of the interval between the multiple cells arranged in the phosphor layer.
In the radiation image acquisition method according to the present invention, the phosphor layer formed of a plurality of cells, arranged in at least the main scanning direction, filled with stimulable phosphor bearing thereon a radiation image is scanned in the main and a sub-scanning direction with a stimulating light beam and the stimulated emission emitted by the phosphor layer due to said scanning is photoelectrically detected as an analog image signal, and said analog image signal is digitized to obtain a digital image signal representing the radiation image; the signal component representing the cell partition walls included in the analog image signal is recognized, and the digital image signal is obtained from the component of the analog signal obtained between the recognized signal components of the cell partition walls.
Note that the expression xe2x80x9carranged in at least the main scanning directionxe2x80x9d refers not to a matrix in which cells are lined up in the main and sub-scanning//vertical and horizontal directions, but to the long straight stripe-shaped cells disposed in the horizontal orientation.
In the radiation image acquisition method according to the present invention, a phosphor having light conversion characteristics different from the stimulable phosphor is mixed with either the cell partition walls or the stimulable phosphor contained therebetween, and the fluorescent light emitted from the phosphor material in the phosphor layer due to aforementioned scanning is detected and the signal component representing the partition walls included in the detected signal can be recognized in this way.
In addition, the signal component representing the partition walls included in the signal obtained by detecting the reflected stimulated light reflected by the phosphor layer due to aforementioned scanning can be recognized.
A mirror surface raising the reflective-index with respect to the stimulating light can be formed on the upper surface of the partition walls.
The cell partition walls can be tinted so that their reflective index with respect to the stimulating light is weakened.
The detected signal component representing the partition walls can be used as a trigger signal for digitizing the analog image signal to obtain the digitized image signal.
In the cell interval detection method of the present invention, the phosphor layer formed of a plurality of cells, arranged in at least the main scanning direction, filled with stimulable phosphor bearing thereon a radiation image is scanned in the main and a sub-scanning directions with a stimulating light and the stimulated emission emitted by the phosphor layer is photoelectrically detected as an analog image signal; the analog signal acquired thereby is then digitized to obtain a digital signal representing the radiation image. The signal component representing the partition walls included in the analog signal is recognized, and based on the thus recognized signal component representing the partition walls, the interval between cells can be obtained.
In the cell interval detection method of the present invention, a phosphor having light conversion characteristics different from the stimulable phosphor is mixed with either the cell partition walls or the stimulable phosphor contained therebetween and the fluorescent light emitted from the phosphor in the phosphor layer due to aforementioned scanning is detected; the signal component representing the partition walls included in the detected signal is recognized, and based on the thus recognized signal component representing the partition walls, the interval between cells can be obtained.
In addition, the signal component representing the partition walls included in the detected signal can be recognized by detecting the reflected stimulated light reflected by the phosphor layer when aforementioned scanning is performed, and based on the thus recognized signal component representing the partition walls, the interval between cells can be obtained.
The radiation image acquisition apparatus of the present invention comprises a phosphor layer formed of a plurality of cells, arranged in at least the main scanning direction, filled with stimulable phosphor bearing thereon a radiation image, a scanning apparatus that scans the phosphor layer in the main and a sub-scanning direction with a stimulating light beam, a detection means that photoelectrically detects as an analog image signal the stimulated emission from the phosphor layer caused by the scanning, a signal acquisition means that digitizes the analog image signal to obtain a digital image signal representing the radiation image; wherein, the detection means recognizes the signal component representing the partition walls included in the analog signal, and obtains the digital image signal from the component of the analog signal obtained between the recognized signal components representing the partition walls.
Either the cell partition walls or the stimulable phosphor contained therein is mixed with a phosphor having light conversion characteristics different from the stimulable phosphor, and the signal acquisition means recognizes the signal component representing the partition walls included in the signal obtained by detecting the fluorescent light emitted from the phosphor material in the phosphor layer due to aforementioned scanning.
The signal acquisition means can recognize the signal component representing the partition walls included in the signal obtained by detecting the reflected stimulating light reflected by the phosphor layer when aforementioned scanning is performed.
A mirror surface raising the reflective-index with respect to the stimulating light can be formed on the upper surface of the partition walls.
The cell partition walls can be tinted so that their reflective index with respect to the stimulating light is weakened.
The signal acquisition means can use the detected signal component representing the cell partition walls as a trigger signal for digitizing the analog image signal.
The digital image signal can also be corrected by being divided by the signal component representing the cell partition walls.
The cell-interval detection apparatus of the present invention comprises: a scanning means that scans in the main and a sub-scanning directions with a stimulating light beam the phosphor layer formed of a plurality of cells, arranged in at least a main scanning direction, filled with stimulable phosphor bearing thereon a radiation image; a detection means that photoelectrically detects as an analog image signal the stimulated emission from the phosphor layer due to the scanning; and a cell interval detection means that recognizes the signal component representing the partition walls included in the analog signal, and based on the thus recognized signal component of the partition walls, obtains the interval between cells.
Either the cell partition walls or the stimulable phosphor contained therein is mixed with a phosphor having light conversion characteristics different from the stimulable phosphor, and the cell interval detection means recognizes the signal component representing the partition walls included in the signal obtained by detecting the fluorescent light emitted from the phosphor material in the phosphor layer due to aforementioned scanning and can obtain the cell interval based on the recognized signal component of the partition walls.
The cell-interval detection apparatus recognizes the signal component representing the partition walls included in the signal obtained by detecting the reflected stimulated light reflected by the phosphor layer when aforementioned scanning is performed, and can obtain the cell interval based on the recognized signal component of the partition walls.
Note that the expression xe2x80x9ca phosphor material having light conversion characteristics different from those of the stimulable phosphorxe2x80x9d refers to a phosphor material that emits light of a wavelength range different from that of the wavelength emitted by the stimulable phosphor when irradiated by the stimulating light beam.
According to the radiation image acquisition method and apparatus of the present invention, the phosphor layer formed of a plurality of cells, arranged in at least the main scanning direction, filled with stimulable phosphor bearing thereon a radiation image is scanned in the main and a sub-scanning directions with a stimulating light beam, and the stimulated emission emitted by the phosphor layer due to the scanning is photoelectrically detected as an analog image signal. In digitizing this analog signal to obtain a digital signal representing the radiation image, the signal component representing the partition walls included in the analog signal is recognized, and because the digital image signal is to be obtained from the component of the analog signal obtained between the recognized signal components of the partition walls, the quantity of stimulated emissions from each cell and the detection value of the quantity of stimulated emissions from each cell can be made to correspond precisely and the analog signal digitized. In this way, the quantity of stimulated emissions within each cell can be obtained precisely as digital image signals.
Note that if a mirror surface that raises reflective-index, with respect to the stimulating light, is formed on the upper surface of the cell partition walls, or if the cell partition walls are subjected to tinting so as to weaken the reflective index thereof, because the difference in intensity of the stimulating light reflected form the cell partition walls and that reflected from the stimulable phosphor can be increased, the signal component representing the cell partition walls can be recognized more accurately.
In addition, if the digital image signal is obtained by using the recognized image signal component representing the cell partition walls as a trigger signal, the quantity of stimulated emissions from each cell and the detection value of the quantity of stimulated emissions from each cell can be made to correspond more precisely and the analog signal digitized, whereby the quantity of stimulated emissions within each cell can be more precisely obtained as digital image signals.
Further, if the value obtained by digitization is corrected by being divided by the signal component representing the cell partition walls, the quantity of stimulated emissions from each cell can be corrected according to the unit of stimulating light scanning distance (the unit length or area).
According to the cell interval detection method and apparatus of the present invention, by recognizing the signal component representing the partition walls included in the analog signal, because the cell interval is obtained based on the thus recognized signal component representing the partition walls, the interval between cell partition walls and the interval of the signal component included in aforementioned analog image signal can be made to correspond precisely and the interval between cells can be detected.